Do you need the 2017 iMac 5K with 4.2GHz Core i7 and Pro 580 GPU to get decent framerates when running the newest versions of serious games? Or will a lesser model with 3.5GHz Core i5 and Pro 575 GPU do just as well?

Total War: WARHAMMER- Using the built-in 'dwarfs versus greenskins' benchmark, we tested using the "High" preset, 2560x1440, full screen.(HIGHER frames per second = FASTER)

X-Plane 11 - Using a recorded 2 minute flight of the SR-71 Blackbird, we launched the most stressful test (fps_test=3) from Terminal app specifying 2560x1440, full screen, circle view. (HIGHER frames per second = FASTER)

How Hot Does The iMac's CPU Get?HWMonitor reported the PECI CPU sensor's maximum reading during the third benchmark run.

How Hard Must The iMac's Fan Work?HWMonitor reported the Main Fan sensor's maximum reading during the third benchmark run.

Assuming both models were configured with 16GB of memory and 1TB Fusion Drive, the 4.2GHz Core i7 model only costs $200 more. If the two games we featured represent the typical gamer's experience, then one must ask, "Is it worth spending 10% more to get 10% better gaming performance?" Probably.

The other deciding factor is heat. There are some who expressed concern that the 17% hotter running Core i7 might not be as reliable in the long term. If you think 212F CPU is hot, the GPU die sensor reported a constant 264F. Activity Monitor reported 30%+ CPU load (or 3 out of 8 hyper-threading cores) when running both Warhammer and X-Plane at our settings. OpenGL Driver Monitor reported 30-40% GPU load for Warhammer and 20%-100% GPU load for X-Plane. (Flying through clouds stressed the GPU most.)

Won't the 16% higher fan speed make the Core i7 model noisier? I suppose that depends on the amount of ambient noise. And if you are a typical hard core gamer that wears headphones, the iMac fan noise under stress is a non-issue.

We disabled* Turbo Boost to measure that effect. The iMac Core i5 3.50 GHz Core i5 with Turbo Boost rated at 4.1GHz (17% increase in clock frequency) gained only 4% in framerate at the expense of 6% gain in CPU temperature.

HOW DOES AN EGPU AFFECT PERFORMANCE AND HEAT? We included the results for the GTX 1080 Ti in the Sonnet eGFX Breakaway Box connected to the TB3 port of the iMac 5K i7. That setup ran as much as 16% faster while the iMac's Core i7 CPU ran 8% cooler and the fan stayed at 1200RPM idle. But, then the eGPU box and 1080 Ti GPU will add $1000 or 33 to 50% to your total system cost --- and that does not include the price of an external display which will be required if you expect the iMac 5K to use the eGPU's card when gaming.